The invention relates to a process for the electrochemical coating of a substrate by brush plating, in which process an electrolyte, in which particles are dispersed, is applied to the substrate using a carrier, wherein a metallic layer, in the matrix of which the particles are incorporated, forms on the substrate.
A process of the type mentioned in the introduction can be gathered, for example, from JP 01301897 A. This document proposes the use of a brush plating process for producing a layer in which particles are dispersed. Brush plating is to be understood as meaning an electrochemical coating process in which the substrate to be coated is not dipped into an electrolyte, but instead the electrolyte is applied to the substrate using a carrier referred to as a brush. More specifically, a brush does not have to be used in this process. Instead, the carrier has to have the properties which make it capable of transferring the electrolyte onto the substrate owing to superior capillary forces. By way of example, a brush is suitable for this purpose because capillary channels suitable for transporting the electrolyte are formed between the individual bristles. Examples of other structures suitable for transferring the electrolyte are sponge-like, i.e. open-pored, inherently elastic materials.
In order to make effective coating possible, the carrier is fed with electrolyte through a channel system, which is fluidically connected to the capillary channels of the carrier. Compared to conventional electrochemical coating, in which the substrate is dipped into the electrolyte, the significant advantage is that a high material throughput is made possible by the continuous feed of electrolyte. During electroplating, for example, correspondingly high deposition currents can accordingly be implemented, and rapid layer build-up is thereby possible. In contrast to electrolyte baths, the continuous flow of the electrolyte in brush plating makes it possible to prevent the establishment of a steady state, which limits the coating rate, in the electrolyte owing to a limited diffusion rate.
It goes without saying that it is also known to incorporate particles in electrochemically produced layers which have been coated in an electrochemical bath. By way of example, it is known according to U.S. Pat. No. 2007/0036978 A1 to incorporate CNTs (this abbreviation is used hereinbelow for carbon nanotubes) in electrochemically deposited layers. However, a factor which further limits the incorporation of the CNTs in this case is the fact that the CNTs can only be dispersed in the electrochemical bath to a limited extent. The production of stable dispersions, i.e. dispersions which also remain stable for a relatively long period of time of more than 24 hours, creates problems. Although it is possible to stabilize the dispersion by using wetting agents, the latter are then also deposited at least partially in the layers. However, an improvement in the conductivity is sought, for example, with the incorporation of CNTs in electrochemical layers. However, the presence of wetting agents, which primarily remain on the surface of the CNTs, restricts the desired effect of the incorporation of CNTs in the metallic matrix of the electrochemically deposited layer.